γ-Amino butyric acid (GABA) is an amino acid conserved from bacteria to plants. It is found in all known plant tissues and the metabolic pathways of GABA synthesis and turnover are well established for the majority of plants. In most cases, GABA is synthesised from glutamate by irreversible action of the enzyme glutamate decarboxylase (GAD). The production of GABA via the GABA shunt is heavily intertwined within the highly regulated and well-studied glutamate pathway. The physiological role of GABA in higher plants has been the subject of much debate.
Dietary intake of GABA is gaining attention due to the fact that it has been associated with a variety of beneficial physiological effects. According to the World Health Organisation, about two thirds of strokes and half the incidence of heart disease are attributable to raised blood pressure. Several studies have suggested that intake of GABA can lower blood pressure and there are claims that ingestion of GABA-rich plants can reduce blood pressure in hypertensive rats (Abe Y et al. (1995). Effect of green tea rich in gamma-amino butyric acid on blood pressure of Dahl salt-sensitive rats. Am. J. Hypertens. 8(1): 74-79). In another more recent study with hypertensive rats a dose of 0.3 to 1.0 mg/kg intra-duodenally administered GABA had a dose-related hypotensive effect, decreasing the blood pressure from 9.20+/−3.96 to 3.50+/−5.34 mmHg (Kimura M, et al., (Yakult) (2002). Involvement of gamma-amino butyric acid (GABA) B receptors in the hypotensive effect of systemically administered GABA in spontaneously hypertensive rats. Japanese Journal of Pharmacology 89(4): 388-94).
GABA is possibly associated with several other health benefits. It is known to be the major inhibitory neurotransmitter in the central nervous system and is therefore thought to have calming properties (Owens, D. F. & Kriegstein, A. R. (2002). Is there more to GABA than synaptic inhibition? Nature Neuroscience 3:715-727). Tea is well known for its relaxing properties, thought to be due to the naturally high levels of GABA (in combination with theanine) “GABA tea” was developed in Japan in 1986 and consists of green tea (naturally higher in GABA) with extra GABA added for relaxation and general well-being.
A diet high in GABA may also have implications for the treatment of the sensory, motor and cognitive declines that accompany old age because GABA modulates neurotransmitter release in the central and peripheral nervous systems (Gordon F and Sved A (2002). Neurotransmitters in central cardiovascular regulation: Glutamate and GABA. Clin. Exp. Pharmacol. P. 29: 522-524). In a recent study, older monkeys that had GABA directly delivered to their neurones responded to visual patterns in the same way as younger monkeys. The study mentions that normal ageing may therefore result in a decreased ability to produce GABA in the cerebral cortex, although this hypothesis is untested (Leventhal A. Et al. (2003). GABA and its agonists improved visual cortical function in senescent monkeys).
Consumers are becoming increasingly aware of the benefits of drinking green tea but may not necessarily associate this with GABA. A number of web-sites advertise health supplements that are high in GABA for lowering blood pressure, decreasing body fat and anxiety relief. Yakult® has launched a milk drink containing GABA known as “Pretio” in Japan (although this is not thought to be present elsewhere in the world) and Lion Corp has recently unveiled a functional beverage known as “Gussumin” based on tomato vinegar derived from fermented tomatoes rich in GABA to target female consumers with sleeping difficulties.
US 2007/0048353 discloses a method of producing food and beverage products with a high content of GABA, wherein processed tomato products are fermented with lactic acid bacteria.
Although most consumers will not be aware of the benefits of GABA, it is envisaged that as consumer awareness grows, there will be an increasing demand for other functional foods high in GABA.
Tomatoes are relatively high in GABA, compared to fresh tea leaves and many other fruit and vegetables, with some varieties being higher than others. Despite existing knowledge of the GABA shunt, up-regulation of GABA in fruits has mainly been achieved through environmental influences, which are difficult to control on a commercial scale.
It is an object of the present invention to provide a process of producing tomato pastes that are high in GABA and that can suitably be used to produce edible processed tomato products that fit into diets that aim to reduce blood pressure, to instil calmness and relaxation and/or to improve sensory, motor and/or cognitive functions.